Can we help Syria without making things worse?

“You smell death everywhere you go,” said a wounded activist last week, describing the Syrian city of Homs, where the regime of Bashar al-Assad has vented its fury on its own people. Horrors in Homs and other cities mount, but the opposition is not cowed. Yet their bravery is not enough: Despite almost a year of protests and regular reports of Assad’s imminent demise, the Syrian dictator remains in power.

The Arab League tried to broker a settlement to ease Assad out but failed, though it may take up the task again. Much of the world signed on to sanctions against Syria, but the economic pain so far is not enough to convince Assad loyalists to abandon the regime. As the body count grows, with hundreds reportedly dying this past week, the Syrian opposition is clamoring for help.

What can the United States do? The Syrian opposition was initially leery of calling for American aid, but as the violence has grown, it has become more open to outside help, asking for “international protection” and calling plaintivelythis month for “everyone around the world to speak up and do something to stop the bloodshed of innocent Syrians.” Some among the opposition have now called for a Libya-style international intervention.

To be of any value, an intervention must end the bloodshed, or at least diminish it dramatically. Syria also must remain an intact state capable of policing its borders, stopping terrorism and providing services to its people. It should not fragment into a failed state, trade Assad for another dictator or become a pawn of foreign powers such as Iran.

As recent U.S. interventions have shown, the United States can be moved to help and advance freedom and its interests in the Middle East — but it can also make things worse or trip over unanticipated consequences. This knowledge should not be an excuse for standing by while Assad slaughters his people, but it should shape how the world responds.

Syria is not Libya. At least, NATO will not carry out a bombing operation there. Russia and China made their opposition clear at the United Nations, voting against a Security Council resolution that called for Assad to step down and asked Syria to withdraw the forces that are mowing down civilians in the country’s cities. Now Syria uses Russia’s anodyne calls for dialogue as a screen to step up repression.

The United States and Europe have little appetite for another war in the Middle East, particularly without U.N. cover. Meanwhile, sanctions are reshaping Syrian politics. Those sanctions, including travel bans and frozen assets, are devastating Syria’s tourism and energy sectors. The value of the Syrian pound is collapsing. All of this places tremendous pressure on Assad.

But sanctions are not a sure thing. In Iraq in the 1990s, similar measures rocked Saddam Hussein’s regime. He recovered, however, and was able to alleviate the economic pressure. He even used the scarcity that the sanctions created to squeeze his opponents and tarnish the international coalition arrayed against him. When Hussein fell, Iraq’s economy was hollow: There was a black market but no free market, and basic services such as electricity lay in ruins. When the United States took over, it had to restart the economy from scratch. Almost a decade later, Iraq has not fully recovered.

Too often, U.S. policy has focused on removing the dictator and not on filling the void that his exit leaves behind. In Egypt, Hosni Mubarak is gone, but the military clings to power. In Iraq, civil war followed Hussein’s fall. The recent departure of Yemen’s President Ali Abdullah Saleh, a move the United States encouraged, has not brought stability to that country. Like Assad, all these dictators undermined their countries’ political and judicial institutions and tried to divide their opponents to stay in power. And with their departures, Iraq, Libya and Yemen all are at risk of becoming failed states.

So it is not enough for Assad to go — the key question is who replaces him. The Syrian opposition is divided by region, sect and political orientation, and the movement fears penetration by regime spies. It is not clear how much, or if, opposition groups outside the country, such as the Syrian National Council, speak for those bearing the brunt of Assad’s repression. One official representing part of the internal opposition told the Guardian newspaper that “the revolution has two arms” and lamented the division between “the people outside, who have no weight on the ground, and the people inside, who are actively leading.”

The Free Syrian Army, an opposition group that embraces armed struggle, claims to “work hand in hand with the people to achieve freedom and dignity,” but rebels battle the regime locally, without central coordination. Activists mock the FSA as the “Facebook Syrian Army” because its leadership is much stronger on the Internet than it is on the ground. This lack of unity may doom postwar Syria. In Libya, the local militias that fought Moammar Gaddafi still operate independently months after his fall, and there is no government that most Libyans accept as legitimate.

The United States also shouldn’t expect gratitude for turning against Assad. In Egypt, where U.S. pressure helped ease Mubarak out, a poll taken after the revolution shows that only a fifth of Egyptians have a favorable view of the United States. The caretaker government run by Egypt’s generals, facing a poor economy and domestic strife, announced that it will try 19 Americans working for nonprofit organizations that promote democracy. Egypt did this in defiance of U.S. warnings that such a prosecution could jeopardize the U.S.-Egypt relationship, including $1.3 billion in military aid.

Whatever the United States decides to do, it won’t be about just Syria. It will be about Russia and Iran, too, countries that are already providing military support to Assad. In Libya, Gaddafi had no friends — his reckless foreign policy had alienated everyone. But in Syria, Western military intervention would only increase Moscow and Tehran’s attachment to Assad.

When the United States invaded Iraq, the country’s neighbors rushed in. Iran in particular sent intelligence and paramilitary personnel to organize locals and at times to fight U.S. forces. In Syria, Iran, working with Lebanon’s Hezbollah, might seek to further help Assad or, should he fall, any remaining allies among regime survivors.

To reduce these risks, the United States and its allies need to build the Syrian opposition into a coherent, representative and legitimate body. A stronger opposition makes it more likely that Assad will fall and puts the United States and its allies — and Syria — in a better position should he do so. Building the opposition may be more important for Syria’s future and U.S. interests than a single-minded focus on removing Assad, who in the end is only a dishonest and brutal leader of an illegitimate and brutal regime.

Militarily, the opposition needs to prove competent enough to stand up to Assad’s tanks and artillery, a tough task for lightly armed and untrained fighters. Even more important, the movement needs to be united. As its ranks come together, the United States should work with its allies to arm and train them. With Turkey, Saudi Arabia and others, the United States should present a cohesive front: using tough love to cajole and reward the opposition for unity and cooperation, while recognizing that some fissures will be inevitable.

Syria is only the latest regime shaken by the Arab uprisings, which have brought freedom and exultation, but also repression and tyranny. However, success in Syria may be more important for the United States than in other countries. The other governments, even Gaddafi’s bizarro-regime, were U.S. allies to varying degrees, and no conflict dragged on as Syria’s has, with no end to the bloodshed in sight. Failure in Syria would set back U.S. security interests as well as deal a blow to fledgling democracies elsewhere in the region. Dictators old and new could take heart that force, again, triumphs in the Middle East.

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Daniel Byman is a professor and the Senior Associate Dean at Georgetown University’s School of Foreign Service and a senior fellow in the Center for Middle East Policy at Brookings. His latest book is “Al Qaeda, the Islamic State, and the Global Jihadist Movement: What Everyone Needs to Know.”